"Alan Murphy" wrote in message
...
"Jim Lesurf" wrote in message
...
In article , Alan Murphy
wrote:
"Jim Lesurf" wrote in message
[big snip to avoid repeating my sequence of questions]

I think it might be clearer, Jim, if I just outline my views on the
subject and hope that you find this acceptable.

I'm afraid that your mode of response does not actually seem 'clearer'
to
me as you have not dealt with the main issue I was specifically asking
you
about. (Please see below.)

I agree that, for the results to be meaningful in AB testing, levels
should be equalised and regret that my devious attempts to wind up
Stewart were misinterpreted.

OK.

I do feel however that AB testing is possibly not a suitable test for
revealing differences close to 1 jnd and is accurate to perhaps 5
jnd.

[snip]

I appreciate that you may "feel" something. I also appreciate that you
might be correct. However, since you seem to be arguing on the basis of
taking an academic approach founded upon applying the scientific method,
my
questions were to invite you to apply this to your own statements.

As for a test to determine whether AB testing is sufficiently
sensitive
to distinguish small audio differences I would propose the following:
It
should be possible to determine minimum audible differences of 1 jnd
over a discrete range of frequencies on a test setup, say from 1000 to
15000Hz at 2000 Hz intervals. A set of digital AB samples to Red Book
CD
standard at normal listening levels would then be prepared, one of
which
would be a pure tone at each of the frequencies and the other would be
the same tone corrupted at alternate values by positive then negative
random increments of digital noise varying from 0 to 5 jnd. My
prediction is that an AB test on these samples would not be able to
distinguish differences of less than 5 jnd. Over to you.

My series of questions was partly to establish if I had understood you
correctly. Partly to establish what test you had in mind that could be
carried out and whose results could distinguish between your hypothesis
that the failure was due to 'masking' and the alternative hypothesis
that
the failure was due to 'removal' of the actual differences.

Unfortunately, your reply does not deal with this point.

I carefully arranged my series of questions so that all but the last
could
be answered fairly quickly and simply with a 'yes' or a 'no'. I would
have
preferred this as it seems clearer to me that your restatement. However
the
key question was the last one (restated above) so I'd like to know your
answer to this. Or do you accept that when you argue that the failure is
due to 'masking' this is no more than a personal belief?

The outline you give from visual experiments is an analogy. This may or
may
not be an appropriate analogy. To test this we would require a response
to
the question which you did not deal with.

So. Can you now say what practical test/experiment you can suggest that
would be useful to test your hypothesis that the failure is due to
'masking' rather than 'removal' of the audible difference?

When I wrote the original post with the term 'masking'
I was not aware that it has a particular meaning and significance
in audio science, not being familiar with the literature. Having
read some relevant papers I now realise that I should have
replaced 'masking' with 'the test is not sufficiently sensitive to
reveal differences which may be present when using some other
method'. My apologies for not being sufficiently clear.

The test that I proposed above would indeed reveal whether the
AB test is insensitive and to what degree, concordant with the
scientific method. I do not have enough knowledge of the subject
to propose a test that would detect low jnd differences in complex
scenarios.

Incidentally during my "googling" I did notice some suggestion that
when different signals are presented simultaneously to seperate ears
much smaller differences can be detected than when these signals are
presented to both ears serially. Any ideas on this?

Alan.


One of the main functions of the hearing system is as a comparator, of
sorts, in order to judge the orientation of the source of sound. So I would
guess the system is particularly sensitive to any differences between
whatever is entering the ears at a given moment in time.